The local progression of primary tumors is extrinsically controlled by type 1 immune responses, particularly via the cytokine IFNgamma, whose secretion is highly dependent on helper T cells. The T-box transcription factor T-bet (Tbx21) plays a critical role in the development of type 1 helper T cells and is essential for the production of IFN?. We have recently published evidence that the T-bet pathway in an autochthonous transgenic mouse prostate adenocarcinoma model exerts a significant suppressor function in the development of metastatic disease. Our overall goal for this funding period is to explore the cellular and molecular mechanisms by which T-bet functions to combat tumors. We will use the TRAMP transgenic model of prostate cancer and a panel of genetic mutant T-bet mice to determine the contributions of T-bet expressing cell types in both the innate and adaptive immune systems in immunity against cancer. However, given the known importance of the Th1 cell in tumor immunity, we will focus most of our efforts on this cell type because there is much we still do not understand about T-bet function in the signature Th cell. The migration of Th1 cells to inflamed sites and their adherence to endothelium is critical to inflammation and to tumor immunity. We have preliminary data that T-bet deficient Th1 cells have an impaired capacity in vitro and in vivo to migrate to and adhere to endothelium presumably by regulating yet to be identified genes in T cells that govern tumor cell migration. Our gene expression analyses in T-bet overexpressing human Th cells identified a series of adhesion/homing receptors controlled by T-bet and three target genes we have identified in the mouse are MlP1alpha, Tim3 and CXCR3. We plan to further explore the defects in T cell migration in T-bet-/- Th1 cells in vivo and to search for additional T-bet target genes by performing a comprehensive scan of human and mouse T-bet promoter binding sites coupled with gene expression analysis in collaboration with Dr. Richard Young at MIT. We recently identified single residues in the T-bet protein whose mutation completely abolishes T-bet function in Th1 cells by unknown mechanisms but perhaps through governing T-bet homodimer and heterodimer formation with proteins yet to be identified. We have discovered that one such protein is the Th2-specific transcription factor GATA-3. We have also discovered that TCR signaling results in T-bet tyrosine phosphorylation at residue 525 by the T cell kinase, Itk. We do not know the function of this phosphorylation event yet in T cells nor do we know whether T-bet is tyrosine phosphorylated in other cell types such as dendritic cells, questions we will explore.